Electromagnetically-induced transparency,slow light,and negative group velocities in a room temperature vapor of 4He1

⁴He¹ at room temperature is a particularly interesting system as velocity changing collisions (VCCs) are necessary to observe ultra-narrow (less than 10 kHz) EIT windows for purely electronic spins in the presence of Doppler broadening. Such narrow resonances are known to be linked to a dramatic reduction of the group velocity of a probe pulse, although the medium is transparent. The evolution of the delay is recorded with respect to the coupling beam intensity and to small Raman detunings. We also demonstrate that it is possible to use optically detuned resonances (Fano-like profiles) to see a transition from slow light to negative group velocity. All these measurements are found to be in good agreement with a simple model based on an effective homogeneous linewidth. To cite this article: F. Goldfarb et al., C. R. Physique 10 (2009).     

Magnetic shielding studies on the alkali molecules Na2 and Cs2 by NMR

NMR in the alkali molecules Na₂ and Cs₂ is performed by the atom-molecule exchange optical pumping method. The shielding differences σ(Na)?σ(Na₂)=(29±16)·10^?6 and σ(Cs)?σ(Cs₂)=(221±12)·10^?6 are obtained. The investigation of the contribution of the valence electron to the magnetic shielding is supported by a NMR experiment in free Cs⁺ ions, which yields the shielding difference σ(Cs)?σ(Cs⁺)=(14±12)·10^?6. These measurements allow an estimation of the spin rotation interaction constant in these molecules.     

Elastische und unelastische Streuung von Elektronen an Gasen

The theoretical differential cross section for the elastic scattering and for the excitation of optical transitions in helium by electron impact has been refined in Born approximation by use of the two parameter Eckart eigenfunction for the ground state and for the excited states. The angular distributions of 25 kev electrons scattered elastically and inelastically by helium were measured in the angular range 2·3·10^?4≦?≦4·10^?2. The intensity distribution of the elastically scattered electrons is in accordance with the theoretical curve for?>7·10^?3 and is disturbed at smaller angles by the primary beam. Normalization of the experimental values to the theoretical elastic differential cross section leads to agreement between the experimental differential cross section for the excitation of the 2¹ P and 3¹ P state and the scattering formulae given in this paper. There are small systematic deviations (<20%) for the 2¹ P differential cross section in the angular range 3·10^?3<?<1·10^?2 only. The oscillator strength of these two transitions has been determined from the scattering measurements:f ₂₁=0·312±0·04 andf ₃₁=0·0898±0·006.     

Self-diffusion in a series of plastic organic solids studied by NMR

Proton nuclear magnetic resonance relaxation times and linewidth measurements have been made on five polycrystalline organic compounds, triethylenediamine, 3-azabicyclononane, norbornane, norbornylene and norbornadiene. Measurements for each sample were made throughout the plastic crystal phase. The results are analysed in terms of molecular motion. Correlation times τ and activation enthalpies for translational self-diffusion of molecules are evaluated: triethylenediamine τ=7·6×10^?19 exp (96·4/RT)s, 3-azabicyclononane τ=1·7×10^?16 exp (83·6/RT)s, norbornane for 131K<T<306 K, τ=4·6×10^?15 exp (54·5/RT)s for 306K<T<360K, τ=1·1×10^?16 exp (64·8/RT)s, norbornylene, τ=4·×10^?15 exp (48·6/RT)s and norbornadiene τ=6·8×10^?15 exp (39·9/RT)s, where R is the gas constant in units of kJ K^?1mol^?1. The results and mechanism of diffusion are discussed in relation to the thermodynamic properties of the materials.     

Second-order doppler-free spectroscopy

The observation of second-order Doppler-free optical resonances with a width of 50 Hz are reported for the first time. It was achieved due to the use of optical selection of cold particles from an absorbing gas. The experiments have been carried out by using a new laser spectrometer, supposed to obtain the saturated absorption resonances with a relative width 10^–13–10^–14. The results of experimental and theoretical studies of second-order Doppler-free effect influence on the shape of nonlinear optical resonances in transit-time conditions are considered.     

Sensitive absorption measurements in the near-infrared region using off-axis integrated-cavity-output spectroscopy

A novel instrument that employs a high-finesse optical cavity as an absorption cell has been developed for sensitive measurements of gas mixing ratios using near-infrared diode lasers and absorption-spectroscopy techniques. The instrument employs an off-axis trajectory of the laser beam through the cell to yield an effective optical path length of several kilometers without significant unwanted effects due to cavity resonances. As a result, a minimum detectable absorption of approximately 1.4×10^-5 over an effective optical path of 4.2 km was obtained in a 1.1-Hz detection bandwidth to yield a detection sensitivity of approximately 3.1×10^-11 cm^-1 Hz^-1/2. The instrument has been used for sensitive measurements of CO, CH₄, C₂H₂ and NH₃. Received: 6 May 2002 / Revised version: 31 May 2002 / Published online: 2 September 2002 RID="*" ID="*"Corresponding author. Fax: +1-650/965-7074, E-mail: d.baer@lgrinc.com     

Narrow resonances of saturated absorption of the asymmetrical molecule CHFCiBr and the possibility of weak current detection in molecular physics

According to V.S. Letokhov's suggestion the neutral and charged weak currents (in weak interactions) must cause a splitting of the vibrational-rotational levels of left and right molecules by a relative value of 10^-15–10^-16. To detect this effect an experiment is proposed which consists of direct measuring the beat frequency of two frequency stabilized lasers, their references being two identical narrow spectral lines in the vibrational-rotational spectrum of two optical isomers of an asymmetrical molecule. For this purpose one may use narrow saturated absorption resonances of CHFClBr induced in the cw CO₂ laser field. The effects having influence on the reproducibility of the frequency by molecular reference and the necessity of identity conditions for cells with left and right molecules (CHFClBr) are discussed.     

A study of hand vibration on chipping and grinding operators,part III: Power levels into the hands of operators of pneumatic tools used in chipping and grinding operations

This paper presents a method for calculating power transmitted to the hands of operators who use vibrating hand tools. Results that relate to a comprehensive multidisciplined NIOSH field study of several hundred chipper and grinder workers who used pneumatic hand tools are presented. The results of this study indicated that the power in the frequency range of 6·3 Hz to 1000 Hz transmitted to the hand ranged from 1·08 × 10³ to 7·23 × 10³ J/s for the chisel and from 8·52 × 10^?1 to 1·57 × 10² J/s for the handle of chipping hammers. For pneumatic grinders the power transmitted to the hands of the tool operators was in the range of 6·58 × 10^?3 to 2·35 × 10^?3 J/s over the same frequency range.     

Estimation of sound velocities from resonance measurements on tungsten carbide calibration spheres

Tungsten carbide spheres have been used as reference targets to calibrate echosounders. The target strength depends upon the longitudinal and transverse stress wave speeds, c₁ and c₂, in the sphere. These may be estimated from the resonance frequencies, which can be measured precisely given two or more resonances whose coupling characteristics are sufficiently different to provide well conditioned equations for these wave speeds. The resonance frequencies may be measured by sampling the echo amplitude or by spectrum analysis. The latter method is more accurate but requires more sophisticated equipment. The measurements have been corrected to remove the bias resulting from the finite bandwidth of the apparatus. Experimental results are given for 11 spheres 38·1 mm in diameter containing a nominal 6% of cobalt binder, procured in two batches from different production runs. Both stress wave speeds are significantly different between but not within the batches, and likewise the sphere density which indicates variation of the cobalt content. For a density of 14 900 kg m^?3 (6% cobalt) and at 11°C, c₁ and c₂ are estimated to be 6853 ± 19 and 4171 ± 7 m s^?1, respectively, within 95% confidence limits. Empirical equations are presented for the speeds as functions of density. The temperature coefficient of c₂ is estimated to be ?1·3 ± 0·6 m s^?1°C^?1. These results demonstrate the high accuracy of the resonance technique for estimating the stress wave speeds in spheres. The small differences observed between the spheres would have a negligible effect on the target strength at 38 kHz.     

Thermal stability and UV–Vis-NIR spectroscopy of a new erbium-doped fluorotellurite glass

A new transparent bulk glass from the system 76TeO₂?·?10ZnO?·?9.0PbO?·?1.0PbF₂?·?3.0Na₂O doped with Er³⁺ (TZPPN doped with Er³⁺) has been prepared using the conventional melt-quenching method. Results of differential thermal analysis (DTA) measurements indicate good thermal stability of this glass. The refractive indices at different wavelengths, the optical energy gap, the Sellmeier gap energy and the dispersion energy have been estimated. The Judd–Ofelt parameters, Ω _t (t?=?2,?4,?6) of Er³⁺ were evaluated from optical absorption spectra. Electric dipole, magnetic dipole type transition probabilities, spectroscopic quality factors, branching ratio and radiative lifetimes of several excited states of Er³⁺ have been predicted using intensity Judd–Ofelt parameters. The spectroscopic properties indicate that TZPPN glass doped with Er³⁺ is a promising candidate for laser applications and may be suitable for upconversion fibre optical devices.     

Recent atomic clock comparisons at NIST

The record of atomic clock frequency comparisons at NIST over the past half-decade provides one of the tightest constraints of any present-day temporal variations of the fundamental constants. Notably, the 6-year record of increasingly precise measurements of the absolute frequency of the Hg⁺ single-ion optical clock (using the cesium primary frequency standard NIST-F1) constrains the temporal variation of the fine structure constant α to less than 2 · 10⁻⁶yr⁻¹ and offers a Local Position Invariance test in the framework of General Relativity. The most recent measurement of the frequency ratio of the Al⁺ and Hg⁺ optical clocks is reported with a fractional frequency uncertainty of ±5.2 · 10⁻¹⁷. The record of such measurements over the last year sensitively tests for a temporal variation of α and constrains , consistent with zero.     

Ferroelectric and optical properties of Ba6Ti2Nb8O30 single crystals

The dielectric, optical and non-linear optical properties of Ba₆Ti₂Nb₈O₃₀ single crystals were examined from room temperature up to the Curie temperature of 245°C. The spontaneous polarization at room temperature was estimated as 0·22±0·01 C/m². The linear electrooptic constants were measured as r₃₃^T=(1·17±0·02)×10^?10 and r₁₃^T=(0·42±0·01)×10^?10 m/V. The non-linear optical coefficients were d₃₃=(15·1±2·0)×10^?12 and d₃₁=(11·0±2·0)×10^?12 m/V, which are comparable to those of Ba₄Na₂Nb₁₀O₃₀. Temperature dependences of δ₃₃ and δ₃₁ (Miller's δ) were found to be proportional to that of P_s.     

Messung der Wirkungsquerschnitte für die Linienverbreiterung von Hochfrequenzübergängen im 63 P 2-Zustand des Quecksilbers durch Stöße mit Edelgasatomen

The linewidth of high frequency transitions between Zeeman-levels of the metastable 6³ P ₂-state of mercury is measured as function of the pressure of various noble gases. The measurements are made for all noble gases in the pressure range from 10^?3 to about 2 · 10^?2 Torr. The cross sections for linebroadening due to atomic collisions are derived from the pressure dependence of the linewidth. These cross sections σ were found to be (71 ± 10) · 10^?16 cm² for He, (82 ± 10) · 10^?16 cm² for Ne, (153± 12) × 10^?16 cm² for Ar, (204±28) · 10¹⁶ cm² for Kr and (291 ± 41) · 10^?16 cm² for Xe.     

Hyperfine fields in erbium metal

The hyperfine Splitting of the 80.6-keVγ transition in Er¹⁶⁶ has been measured in erbium metal between 4.2 °K and 40 °K using the Mössbauer effect. There is evidence for a unique magnetic field and electric fieldgradient at all nuclei in erbium metal. The magnetic field decreases from (7.55±0.20)·10⁶ Oe at 4.2 °K to (6.10±0.40)·10⁶ Oe at 40 °K. Extrapolation to 0 °K yieldsH (0 °K)=(7.60±0.20)·10⁶ Oe. The quadrupole interaction energy for the 80.6-keV state iseQ V _Z′Z′/4=(0.95±0.20)·10^?6 eV at 4.2 °K. These results are discussed and compared with other measurements.     

Magnetic susceptibility of lead sulphide

Magnetic susceptibility measurements were carried out on lead sulphide in the form of natural galena crystals, and in the form of crushed powder. The experimental molecular diamagnetic susceptibility value was found to be 93·27×10^?6 (in e.m.u./gm.mol.) for the single crystal and 81·84×10^?6 for the powdered material. Calculations based on a modified Slater-Angus method showed that the type of bonding is mainly covalent with a partial ionic character.     

Relation between relaxation losses in domain-wall motion and ferromagnetic resonance in garnet films

Domain-wall mobility has been studied in garnet films having perpendicular magnetic anisotropy and a narrow FMR line. An analysis of the obtained and published experimental data shows that for the value of the Landau-Lifshits reduced damping parameter derived from FMR measurements, Λ_FMR>2.4×10⁻⁹ Oe²·s, the domain-wall mobility is inversely proportional to Λ_FMR, which is in agreement with classical theory. For Λ_FMR<2.43×10⁻⁹ Oe²·s, the mobility decreases with decreasing Λ_FMR. Possible reasons for this behavior are discussed. An empirical expression relating the losses entailed in domain motion to FMR-related losses for small Λ_FMR is proposed. Fiz. Tverd. Tela (St. Petersburg) 40, 1519–1525 (August 1998)     

Size effect on the conduction electron spin resonance of small sodium particles in sodium azide NaN3

The conduction electron spin resonance from small (10 to 1000 Å sodium metal particles has been measured as a function of the particle size. The particles were formed inside single crystals of sodium azide by X-irradiating and annealing them at 280°C. The particle sizes were deduced from the optical absorption measurements reported in the previous article. According to the theory of the quantum size effect in small metal particles, very narrow resonances should have been observed. No such resonances were seen. The measured widths were between 7.5 and 20 G and could be analysed in terms of the bulk width plus a temperature independent but size dependent surface term. The reason why no quantum size effect was observed is not understood.     

Dipolar studies in CaF2 with Ce3+

Dielectric relaxation in CaF₂ doped with various amounts of Ce³⁺ (0·01 to 1·0 mol%) was measured. The value of the activation energy for orientation of the dipoles {Ce³⁺-F^? interstitial} was determined to be H = (0·46 ± 0·01) eV. The frequency factor was found to have the value τ_o = (5 ± 1) × 10^?15 sec, giving for the vibrational frequency of the interstitial the value ν_o = (5 ± 1) × 10¹³ sec^?1.The number of dipoles contributing to the dielectric loss peak was determined to be between 10¹⁷ and 8 × 10¹⁷ cm^?3 for the different doping amounts of Ce³⁺. Optical absorption measurements showed the existence of large aggregate bands. We could verify that there exists a second-order reaction of aggregation, which is responsible for the non-linearity found between optical absorption at 305 nm and the nominal concentration of Ce³⁺ in the samples. On the other hand, if we assume that the centers which contribute to optical absorption at 305 nm are those also responsible for the relaxation peak, we find that the number contributing to each process is not the same. We can define an interaction radius R as the minimum separation between two dipoles allowing them to contribute to the relaxation peak. From our experimental data R ? 3·8 × 10^?7 cm.     

Die Diffusionskoeffizienten und mittleren freien Weglängen der geladenen und neutralen Radon-Folgeprodukte in Luft

The knowledge of the diffusion coefficients of radioactive atoms and ions in air is very important in a number of investigations on and computations of the attachment of radon decay products to aerosol particles. In this work measurements of the diffusion coefficients of neutral and charged²¹²Pb atoms are reported. The values found areD ₀=(7.6±0.4)·10^?2cm²s^?1 for neutral atomsD=(5.0±0.3)·10^?2cm²s^?1 for charged atoms The used method of measurement allowed to determine these constants 1–5 seconds after the formation aged²¹²Pb atoms, so that a “cluster” formation was improbable. The mean free path for neutral (λ₀=(4.9±0.3)·10^?6cm) and charged (λ=(3.2±0.2)· 10^?6cm) lead 212 atoms in air were computed from the measured diffusion coefficients. All obtained results were compared with values, calculated from theory.     

The quadrupole moments of carbon dioxide and carbon disulphide

The electric quadrupole moments of carbon dioxide and carbon disulphide have been measured through the birefringence induced in gaseous samples over a range of temperature. The value for CO₂, Θ = (-14·98 ± 0·50) × 10^-40 C m², is consistent with earlier measurements, showing that the temperature-independent hyperpolarizability contribution to the birefringence is insignificant. For CS₂, Θ = (+12·0 ± 0·6) × 10^-40 C m². The positive sign reflects the increased importance of the π electron contribution to Θ in CS₂.